Rigid polyurethane foams containing lithium salts for energy absorbing applications

ABSTRACT

The present invention relates to using lithium salts of an organic material having 2 to 30 carbon atoms and at least one carboxylic acid in a rigid polyurethane formulation to produce foams having energy absorbing properties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to energy absorbing rigid polyurethane foamcompositions and their methods of preparation. Specifically, the energyabsorbing rigid polyurethane compositions of this invention are waterblown and employ lithium salts to promote cell opening, enabling thefoam to exhibit minimal spring back or hysteresis. Such foams aresuitable as lightweight alternatives to traditional energy absorbingapplications, such as side impact bolsters in automobile doors and foamblocks for floral arrangements.

2. Description of the Related Art

Recent years have seen an accelerated growth in the field of energyabsorbing foams, especially in the automotive industry. Heightenedsafety concerns over the safety of passengers has generated numerousfederal safety standards, among which are passive restraint systems suchas air bags. As pointed out in "Fundamental Studies of Polyurethane Foamfor Energy Absorption in Automotive Interiors" by J. A. Thompson-Colon,et al. in SAE Technical Paper Series 910404, the advent of air bags hasrequired the automotive industry to look to the manufacture of energyabsorbing instrument panels, or knee bolsters, since one tends to slideunder a deployed air bag and impact the knee on the panel. Also,currently under study is the use of energy absorbing foams as hip orshoulder bolsters to protect the hip and shoulder regions of a passengeror driver against impacts during collisions to the side of the car.

One of the requirements of a good energy absorbing foam is that it isopen celled and exhibits a constant or nearly constant compressivestrength at deflections ranging from about 10 percent to about 60percent. Upon impact, the cell struts and walls crush and therebydissipate the energy of the impacting object. Air trapped within aclosed-celled foam, however, imparts structural strength to the wallsand struts upon compression resulting in a resilient foam that exhibitsan exponential increase in compressive strength upon continueddeflection through the foam. Thus, it is desirable to open the cells ofthe foam as much as possible.

As is discussed in detail in the description of the invention, it hasnow been found that the use of lithium salts of an organic acidapparently open the cells of rigid polyurethane foams. The use oflithium salts as catalysts in CFC-blown rigid polyurethane foams isknown from such U.S. patents as U.S. Pat. No. 4,107,069, which describesa lithium, sodium or potassium salt of a 2-20 carbon atom carboxylicacid chain as a gel catalyst to preserve the reactivity of aCFC-containing masterbatch for rigid polyurethane foams; U.S. Pat. No.4,256,847 which describes a mixture of lithium and zinc salts tocatalyze rigid foam systems blown by CFCs with the sole use of lithiumsalts as catalysts discouraged due to their high catalytic activity;U.S. Pat. No. 3,108,975 which describes a mixture of alkali metalhydroxides and alkali metal salts of acids as a catalyst for theproduction of polyurethane foams blown with high quantities of water,the only examples being that of flexible foams having resiliency and theabsence of the hydroxide failing to produce a foamed product; U.S. Pat.No. 3,041,295 which describes a chlorinated phosphate ester containingpolyurethane foam (flexibles exemplified) blown with high quantities ofwater by incorporating a lithium salt into the prepolymer to preservethe foam against humidity breakdown; U.S. Pat. No. 3,634,345 whichdescribes the use of alkali metal salts of o-hydroxycarboxylic acids asa catalyst to polymerize the isocyanate into isocyanurate rings in acoating, elastomer, or foam blown with 5 to 50 parts CFC and optionallywater; U.S. Pat. No. 3,769,245 which describes the use of alkali metalsalts of carboxylic acids to catalyze the reaction of a dicarboxylicacid with the isocyanate group to release carbon dioxide and produce athermoplastic polyurethane foam blown in the absence of water; U.S. Pat.No. 3,940,517 which describes alkali metal salts as catalysts in theproduction of polyisocyanurate foams blown with CFCs, and U.S. Pat. No.5,084,485 which describes using an alkali metal carboxylate (onlypotassium acetate mentioned) as a trimerization catalyst in anisocyanurate foam blown with water to yield a closed cell insulationboard. In each of these patents, however, the alkali metal salts areemployed as catalysts; and none describe energy absorbing properties ofa foam. The above patents also describe the production of CFC-blownfoams, large water content blown foams, high density foams, resilientfoams, predominately polyisocyanurate and closed celled foams, orthermoplastic foams.

Examples of described energy absorbing foams are found in variouspatents and publications. U.S. Pat. No. 4,866,102 describes moldableenergy absorbing rigid polyurethane foam compositions which are preparedby the reaction of a graft polymer dispersion in a polyoxyalkylenepolyether polyol with an alkylene oxide adduct of toluenediamine ordiaminodiphenylmethane with an organic polyisocyanate in the presence ofa crosslinking agent and a chlorofluorocarbon (CFC) blowing agent. Otherpatents describe energy absorbing foams which are flexible orsemi-rigid, are resilient, have utility in bumper cores, and have moldeddensities in excess of 5 pcf, such as U.S. Pat. Nos. 4,190,712,4,116,893; 4,282,330; and 4,212,954. The foams described in thesepatents, although employing the phrase "energy absorbing," are notuseful for the purposes of this invention since they exhibit resiliencyor recovery. The foams of this invention are rigid and crush uponimpact, exhibiting little or no rebound, and preferably have moldeddensities of less than 2.8 pcf. U.S. Pat. No. 4,722,946 describes theproduction of energy attenuating viscoelastic polyurethane elastomersand foams, rather than rigid foams, comprising mixtures of linear andbranched polyol intermediates, polyisocyanates, and optionally,extenders, blowing agents, and the like, in the presence of a catalystwhereby the isocyanate index is varied from about 65 to about 85. U.S.Pat. No. 4,664,563 describes a method of shoring a geological formationwhich comprises preparing a high density (19 pcf-50 pcf) rigidpolyurethane foam having a specific oxyalkylated toluenediamine as thepolyol, which exhibits nearly constant strain with increasing stress incompression. Similarly, U.S. Pat. No. 4,614,754 described a high density(>17 pcf) rigid polyurethane foam which exhibits nearly constant strainwith increasing stress in compression at high loadings (>600 psi) byreacting a specific alkoxylated toluene diamine. Again, the foam must beprepared by using a specific polyol; and foams with such high densitiesand high loadings at yield are not usable for the automotive interiorapplications described above or as floral foams. U.S. Pat. No. 4,696,954describes the preparation of high density (>25 pcf) molded polyurethanefoams blown with CFCs characterized by high impact strength and goodthermal stability.

SUMMARY OF THE INVENTION

It is an object of the invention to manufacture foams having energyabsorbing properties utilizing a wide range of polyols commonly employedin the preparation of rigid foams. It is another object of the inventionto substitute an environmentally safe blowing agent in the production oflow density rigid polyurethane foams for traditional chlorofluorocarbonswhile retaining energy absorbing properties. It is still another objectof the present invention to manufacture a low density molded rigidpolyurethane foam having energy absorbing properties, also molded at lowpacking ratios. A final object of the invention is to produce an energyabsorbing foam having a density of less than 2.8 pcf employing less than8 parts by weight water without the aid of CFCs. The characteristics ofthe more preferable foams of the invention for interior automotiveapplications are:

1. Constant or nearly constant compressive strengths at 10 percent to 60percent deflection;

2. Blown without the aid of any blowing agent besides reactive blowingagents and employing less than 8 parts by weight of reactive blowingagents;

3. Low density;

4. Little or no limitation on the polyol employed as long as the polyolis suitable for manufacture of rigid foams; and,

5. Low packing ratios.

It has now been found that constancy of the strain exhibited by a foamundergoing deflection is improved by adding a lithium salt of an organicmaterial having at least one carboxylic acid to a wide variety ofreactive blown rigid polyurethane foam formulations. The water blownrigid polyurethane foams of the invention exhibit constant or nearlyconstant compressive strengths at low densities without the necessity ofutilizing high pressure molding techniques or high packing ratios. Sincethe lithium salts apparently act as cell opening agents, one also neednot use the high amounts of water typically employed to effectsufficient blowing to open up the cells.

The polyurethane foams of the instant invention find utility inapplications requiring energy absorption, such as shoulder bolsters andhip bolsters in automobiles, and floral foams. The foams havepredominately polyurethane linkages. The foams can be water blown usingless than 8 parts by weight water to achieve densities lower than 2.2pcf without the aid of volatile hydrocarbon or chlorofluorocarbonblowing agents. Reducing the amount of water employed to prepare lowdensity foams has several advantages, including materials savings sincethe amount of isocyanate consumed by water is reduced, equipment savingssince molds with a lower clamping force can be employed, and safetyimprovements during molding due to lowered molding pressures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates four curves corresponding to Samples 1-4, with Sample1 representing a foam without lithium stearate, and Samples 2-4represent foams made with different amounts of lithium stearates.

FIG. 1A illustrates seven curves representing the compressive strengthsof foams undergoing deflection made with a variety of polyols.

FIG. 2 illustrates five curves representing different water blown foamsmade with lithium acetate exhibiting constant or nearly constantcompressive strengths.

FIG. 2A illustrates seven large sloped curves representing water blownfoams made without lithium stearate.

FIG. 3 illustrates six curves representing water blown foams made withlithium acetate by the machine mixing and molding technique havingconstant or nearly constant compressive strengths while undergoingdeflection.

FIG. 4 illustrates six curves showing the constancy of foams made withdifferent polyols and lithium acetate, and foams made with lithiumacetate dissolved in formic acid.

FIG. 4A illustrates six curves showing the constancy of foams made withdifferent polyols and lithium acetate, and foams made with lithiumacetate dissolved in formic acid.

FIG. 5 illustrate the large sloping curves of foams made with no lithiumsalts or undissolved lithium salts.

FIG. 5A illustrates six curves representing the constancy in compressivestrength of six foams having the same composition as the foams of FIG. 5but made with lithium acetate.

FIG. 6 illustrates four curves representing additional embodiments offoams made with lithium acetate exhibiting constant or nearly constantcompressive strengths.

DETAILED DESCRIPTION OF THE INVENTION

It has been found that a lithium salt of an organic material having atleast one carboxylic acid group added to rigid polyurethane foamformulations employing low levels of reactive blowing agents and a widevariety of polyols, molded at low packing ratios, produced foams havingconstant or nearly constant compressive strengths. The mechanism bywhich this phenomena occurs is not completely understood, but it appearsthat the lithium salt acts as a cell opening agent. Without beinglimited to a theory, it is believed that either the lithium salt causesslight deformations in the cell windows during the exothermic foamingprocess, thereby causing the windows to rupture at much lower internalpressure, or that the lithium salt embrittles the struts to such adegree that they readily collapse at uniform forces even with closedcells. By opening the cells of the rigid polyurethane foam, an objectpenetrating the foam crushes the struts of an empty cell rather thancrushing cell struts supported by trapped gases. Upon furtherinvestigation, however, it was also unexpectedly found that sodium orpotassium acetates or stearates failed to yield adequate energyabsorbing foams, a possible explanation being that the sodium andpotassiums salts may predominately deposit along the struts of the cellrather than the cell window perhaps due to their larger atomic radii.

The organic material of the lithium salt includes saturated orunsaturated aliphatic, cycloaliphatic, or aromatic carboxylic acidshaving from 2 to 30, preferably 2 to 19 carbon atoms inclusive of thecarboxylic acid carbon atom. Suitable carboxylic acids include aceticacid, stearic acid, oleic acid, lauric acid, benzoic acid, and the like,preferably aliphatics, and more preferably acetic acid. To reduce theopportunity for extraneous reactions with the isocyanate, the number ofcarboxylic acid groups is preferably one. However, the carboxylic acidmay contain more than one carboxylic acid group as, for example, citricacid.

The amount of lithium salt contained in the formulation is from 0.01 pbwto about 5.0 pbw, preferably 0.01 pbw to about 3 pbw, more preferably0.1 pbw to 2 pbw, most preferably 0.5 pbw to 1.0 pbw, based on 100 partsby weight of polyol. The term "polyol" when used as a reference againstwhich other ingredients are measured throughout the disclosure refers tocompounds having at least two isocyanate reactive hydrogens, includingchain extenders but excluding water and catalysts. Although one mayexceed amounts greater than 3.0 pbw, there is no further noticeableimprovement in constant compressive strength characteristics.

The lithium salt containing energy absorbing polyurethane foams of thisinvention may be blown with reactive blowing agents, physically activeblowing agents excluding hard or fully halogenated chlorofluorocarbons,or a mixture of the two kinds of blowing agents.

In one preferable embodiment of the invention, the polyurethane foam iscompletely blown by reactive blowing agents. The phrase "reactiveblowing agent" is meant herein as a blowing agent other than aphysically active blowing agent such as volatile hydrocarbons, softchlorofluorocarbons (HCFCs), and fully halogenated hydrocarbons known ashard CFCs. A completely reactive blown foam is one which altogetherexcludes the presence of the aforementioned physical blowing agents fromthe foam system.

The phrase "reactive blowing agents" is meant, however, to includechemically reactive blowing agents such as, but not limited to, water, amixture of water and formic acid, or tertiary alcohols. Formic acid maybe added to the resin side as an acid, premixed with the lithium salt,or as a salt dissolved in water. If formic acid or a mixture of premixedformic acid and lithium salt is added, it is preferable to employ 96%aqueous formic acid solution to passivate the metal in molding machinesand avoid the rapid corrosion caused by dilute concentrations. A 96%formic acid solution or other aqueous solutions having lowerconcentrations of formic acid are deemed to be a mixture of formic acidand water. The foam of this invention may also be water blown, meaning afoam system blown without the aid of any other reactive or physicalblowing agent.

In another embodiment of the invention, the polyurethane foams can beblown solely with volatile hydrocarbons, soft CFCs each having a boilingpoint below 28° C. and above -60° C. and which vaporize at or below thetemperature of the foaming mass, volatile fluorinated organic compounds,or with a mixture of these physical blowing agent(s) and reactiveblowing agent(s). Volatile hydrocarbons include butane, pentane, hexane,heptane, cyclopentane, cyclohexane, pentene, and heptene. Soft CFCs aredefined as having at least one hydrogen atom and an ozone depletionpotential of less than 0.2, and include 1,1,1-trichlorethane, HCFC-141b,HCFC-22, HCFC-123, and HCFC-142. In another embodiment, a mixture ofphysical blowing agents, excluding hard CFCs, and reactive blowingagents may be employed. Preferably, the quantity of reactive blowingagent predominates in a mixture with physical blowing agent(s). As theratio of physical blowing agent to reactive blowing agent increases in amixture, the total amount of blowing agent required to make a foam at agiven density also increases.

The amount of physical blowing agent present, whether used as the soleblowing agent or in a mixture, need not exceed 20 parts by weight basedon 100 parts by weight polyol. The amount of reactive blowing agentadded in a completely reactive blown foam is effective to blow thepolyurethane foam to a density less than or equal to 2.8 pcf formanufacturing bolsters and floral foams. The invention also finds use inother applications requiring a foam with densities greater than 3 pcf,such as the aforementioned 19-50 pcf foams for shoring geologicalformations. The advantage of the invention is that by using lithiumsalts the cells of the foam open requiring less blowing agent to achievethe desired density, it yields a foam with a constant or nearly constantcompressive strength, and the foam is not limited to a specific polyol.

The amount of water in the system ranges from 0.01 parts by weight to8.0 parts by weight based on 100 parts by weight of polyol. To achievemolded or free rise densities of less than 2.8, only about 8 parts byweight, preferably less than about 7.5 parts by weight, more preferablyless than about 7.0, most preferably less than 6.5 and as low as about4.5 parts by weight or less of water based on 100 parts by weight of thepolyol need be employed in water blown systems. When formic acid and/orsalts thereof are added along with water as blowing agents, the amountof water need only be about 0.01 parts by weight to about 5.0 parts byweight, preferably 0.7 to 3.0 parts by weight, more preferably about 0.8to about 1.5 parts by weight, based on 100 parts by weight of polyol toattain molded or free rise parts having a density of less than 2.8 pcf.

At the above described quantities of water, polyurethane foams having anopen cell structure can be molded at densities of 2.8 pcf or less,preferably less than about 2.3 pcf, more preferably less than about 2.2pcf, most preferably less than 2.0 pcf, with a preferable range beingabout 1.9 pcf to about 2.2 pcf. Such low molded densities can beattained at the above described low water or water/formic acid mixturequantities by adding small amounts of lithium salts. Instead of packingthe mold with large amounts of polyurethane or large amounts of water toeffect the "overblowing" necessary to open up the cells, it is believedthe lithium salt aids in opening the cells as a cell opening agentadvantageously allowing one to use reduced quantities of water to obtainan open celled foam. Free rise densities of less than 2.2 pcf,preferably less than 2.0 pcf, more preferably less than 1.5 pcf, canalso be attained at these low water levels and even lower levels whenformic acid is admixed, by incorporating lithium salts into the resinside.

The rigid energy absorbing polyurethane foams of the inventionpreferably exhibit constant or nearly constant compressive strengths atdeflections from about 10 percent to about 60 percent and at loads ofless than 60 psi; preferably less than 50 psi. The word "constant" isdefined herein as a deflection/compressive strength curve which does notdeviate more than ±6 psi on either side of the curve at deflectionsranging from 10 percent to 60 percent, using the compressive strengthmeasured at 10 percent deflection as the reference point. Preferably,the constancy of compressive strength has a deviation of less than ±5psi, more preferably less than ±4 psi, most preferably less than about±3 psi. A "nearly constant" compressive strength is defined as acompressive strength curve which does not deviate more than ±10 psi oneither side at deflections ranging from 10 percent to 60 percentmeasured as described above. In some foam formulations, such as thosemade with lithium stearate, the deviation will be greater than ±10 psi;nevertheless, foams produced from these formulations exhibit smallerdeviations in compressive strengths and better energy absorbingproperties than the identical foams made without lithium salts.

The type of isocyanate or isocyanate reactive compounds employed toobtain an energy absorbing polyurethane foam is not restricted to anarrow range of polyols or isocyanates. The lithium salts describedherein are employed in a wide variety of rigid polyurethane foamsprepared by the reaction of organic polyisocyanate with a compoundhaving at least two isocyanate reactive hydrogens in the presence of ablowing agent, a urethane promoting catalyst, and a surfactant. Thereaction is carried out at an index ranging from 60 to 400, preferably60 to less than 150 to promote polyurethane linkages.

Suitable examples of the compound having at least two isocyanatereactive hydrogens include polyols such as polyoxyalkylene polyetherpolyols, polyoxyalkylene polyester polyols, and graft polyols;polyhydric polythioethers; polyhydroxyl-containing phosphorouscompounds; polyacetals; and aliphatic thiols. These compounds have anaverage functionality of about 2 to 8, preferably about 3 to 8, atheoretical hydroxyl number from about 300 to about 700, and equivalentweights ranging from about 50 to about 1500, preferably 70 to about 150.

Suitable hydroxy-terminated polyester include those obtained, forexample, from polycarboxylic acids and polyhydric alcohols. A suitablepolycarboxylic acid may be used such as oxalic acid, malonic acid,succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid,azelaic acid, sebacic acid, brassylic acid, thapsic acid, maleic acid,fumaric acid, glutaconic acid, α-hydromuconic acid, β-hydromuconic acid,α-butyl-α-ethyl-glutaric acid, α,β-diethylsuccinic acid, isophthalicacid, therphthalic acid, phthalic acid, hemimellitic acid, and1,4-cyclohexanedicarboxylic acid. A suitable polyhydric alcohol may beused such as ethylene glycol, propylene glycol, trimethylene glucol,1,2-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol,hydroquinone, resorcinol glycerol, glycerine, 1,1,1-trimethylol-propane,1,1,1-trimethylolethane, 1,2,6-hexanetriol, α-methyl glucoside, sucrose,and sorbitol. Also included within the term "polyhydric alcohol" arecompounds derived from phenol such as 2,2-bis(4-hydroxyphenyl)-propane,commonly known as Bisphenol A.

Suitable polyoxyalkylene polyether polyol may be used such as thepolymerization product of an alkylene oxide with a polyhydric alcohol.Suitable polyhydric alcohols include those disclosed above for use inthe preparation of the hydroxy-terminated polyesters. Any suitablealkylene oxide may be used such as ethylene oxide, propylene oxide,butylene oxide, amylene oxide, and mixtures of these oxides. Thepolyalkylene polyether polyols may be prepared from other startingmaterials such as tetrahydrofuran and alkylene oxide-tetrahydrofuranmixtures; epihalohydrins such as epichlorohydrin; as well as aralkyleneoxides such as styrene oxide. The polyalkylene polyether polyols mayhave either primary or secondary hydroxyl groups. Included among thepolyether polyols are polyoxyethylene glycol, polyoxypropylene glycol,polyoxybutylene glycol, polytetramethylene glycol, block copolymers, forexample, combinations of polyoxypropylene and polyoxyethylene glycols,poly-1,2-oxybutylene and polyoxyethylene glycols, poly-1,4tetramethyleneand polyoxyethylene glycols, and copolymer glycols prepared from blendsor sequential addition of two or more alkylene oxides. The polyalkylenepolyether polyols may be prepared by any known process such as, forexample, the process disclosed by Wurtz in 1859 and Encyclopedia ofChemical Technology, Vol. 7, pp. 257-262, published by IntersciencePublishers, Inc. (1951) or in U.S. Pat. No. 1,922,459. Polyethers whichare preferred include the alkylene oxide addition products oftrimethylolpropane, glycerine, sucrose, sorbitol, propylene glycol,dipropylene glycol, pentaerythritol, and2,2-bis(4-hydroxyphenyl)-propane and blends thereof having equivalentweights of from 100 to 5000.

Suitable amines which may be condensed with alkylene oxides includearomatic amines such as aniline, N-alkylphenylenediamines, 2,4'-, 2,2'-,and 4,4'-methylenedianiline, 2,6- or 2,4-toluenediamine, vicinaltoluenediamines, o-chloro-aniline, p-aminoaniline,1,5-diaminonaphthalene, methylene dianiline, the various condensationproducts of aniline and formaldehyde, and the isomeric diaminotoluenes;and aliphatic amines such as mono-, di-, and trialkanolamines, ethylenediamine, propylene diamine, diethylenetriamine, methylamine,triisopropanolamine, 1,3-diaminopropane, 1,3-diaminobutane, and1,4-diaminobutane Preferable amines include monoethanolamine, vicinaltoluenediamines, ethylenediamines, and propylenediamine.

Suitable polyhydric polythioethers which may be condensed with alkyleneoxides include the condensation product of thiodiglycol or the reactionproduct of a dicarboxylic acid such as is disclosed above for thepreparation of the hydroxyl-containing polyesters with any othersuitable thioether glycol.

The hydroxyl-containing polyester may also be a polyester amide such asis obtained by including some amine or amino alcohol in the reactantsfor the preparation of the polyesters. Thus, polyester amides may beobtained by condensing an amino alcohol such as ethanolamine with thepolycarboxylic acids set forth above or they may be made using the samecomponents that make up the hydroxyl-containing polyester with only aportion of the components being a diamine such as ethylene diamine.

Polyhydroxyl-containing phosphorus compounds which may be used includethose compounds disclosed in U.S. Pat. No. 3,639,542. Preferredpolyhydroxyl-containing phosphorus compounds are prepared from alkyleneoxides and acids of phosphorus having a P₂ O₅ equivalency of from about72 percent to about 95 percent.

Suitable polyacetals which may be condensed with alkylene oxides includethe reaction product of formaldehyde or other suitable aldehyde with adihydric alcohol or an alkylene oxide such as those disclosed above.

Suitable aliphatic thiols which may be condensed with alkylene oxidesinclude alkanethiols containing at least two --SH groups such as1,2-ethanedithiol, 1,2-propanedithiol, 1,2-propanedithiol, and1,6-hexanedithiol; alkene thiols such as 2-butene-1,4-dithiol; andalkyne thiols such as 3-hexyne-1,6-dithiol.

Also suitable as the polyol are polymer modified polyols, in particular,the so-called graft polyols. Graft polyols are well known to the art andare prepared by the in situ polymerization of one or more vinylmonomers, preferably acrylonitrile and styrene, in the presence of apolyether or polyester polyol, particularly polyols containing a minoramount of natural or induced unsaturation. Methods of preparing suchgraft polyols may be found in columns 1-5 and in the Examples of U S.Pat. No. 3,652,639; in columns 1-6 and the Examples of U.S. Pat. No.3,823,201; particularly in columns 2-8 and the Examples of U.S. Pat. No.4,690,956; and in U.S. Pat. No. 4,524,157; all of which patents areherein incorporated by reference.

Non-graft polymer modified polyols are also preferred, for example,those prepared by the reaction of a polyisocyanate with an alkanolaminein the presence of a polyol as taught by U.S. Pat. Nos. 4,293,470;4,296,213; and 4,374,209; dispersions of polyisocyanurates containingpendant urea groups as taught by U.S. Pat. No. 4,386,167; andpolyisocyanurate dispersions also containing biuret linkages as taughtby U.S. Pat. No. 4,359,541. Other polymer modified polyols may beprepared by the in situ size reduction of polymers until the particlesize is less than 20μm, preferably less than 10μm.

Organic polyisocyanates which may be employed include aromatic,aliphatic, and cycloaliphatic polyisocyanates and combinations thereof.Representative of these types are the diisocyanates such as m-phenylenediisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate,mixtures of 2,4- and 2,6-toluene diisocyanate, hexamethylenediisocyanate, tetramethylene diisocyanate, cyclohexane-1,4-diisocyanate,hexahydrotoluene diisocyanate (and isomers),naphthalene-1,5-diisocyanate, 1-methoxyphenyl-2,4-diisocyanate,4,4,-diphenylmethane diisocyanate, mixtures of 4,4,- and2,4,-diphenylmethane diisocyanate, 4,4,-biphenylene diisocyanate,3,3,-dimethoxy-4,4,-biphenyl diisocyanate, 3,3,-dimethyl-4,4,-biphenyldiisocyanate and 3.3,-dimethyldiphenylmethane-4,4,-diisocyanate; thetriisocyanates such as 4,4',4"-triphenylmethane triisocyanate, andtoluene 2,4,6-triisocyanate; and the tetraisocyanates such as4,4'-dimethyldiphenylmethane-2,2'-5,5'-tetraisocyanate and polymericpolyisocyanates such as polymethylene polyphenylene polyisocyanate, andmixtures thereof. Especially useful due to their availability andproperties are 4,4'-diphenylmethane diisocyanate, polymethylenepolyphenylene polyisocyanate, or mixtures thereof for rigid foams, or amixture of the foregoing with toluene diisocyanates for semi-rigidfoams.

Crude polyisocyanates may also be used in the compositions of thepresent invention, such as crude toluene diisocyanate obtained by thephosgenation of a mixture of toluenediamines or crude diphenylmethaneisocyanate obtained by the phosgenation of crude diphenylmethanediamine. The preferred or crude isocyanates are disclosed in U.S. Pat.No. 3,215,652.

The constant or near constant compressive strengths, low densities, andlow water content are features achieved by adding lithium salts withoutthe necessity for using chain extending agents besides the low amountsof water used for blowing. Thus, chain extenders are optional, and thosewhich may be employed in the preparation of the polyurethane foamsinclude compounds having at least two functional groups bearing activehydrogen atoms such as hydrazine, primary and secondary diamines, aminoalcohols, amino acids, hydroxy acids, glycols, or mixtures thereof. Thephrase "chain extenders" used herein is not meant to include water. Apreferred group of chain-extending agents, if used, includes diethyleneglycol, 1,4-butanediol and primary and secondary diamines such asphenylene diamine, 1,4-cyclohexane-bis-(methylamine), ethylenediamine,diethylenetriamine, N-(2-hydroxypropyl)ethylene-diamine,N,N'-di(2-hydroxypropyl)ethylenediamine, piperazine, and2methylpiperazine.

Any suitable urethane promoting catalyst may be used including tertiaryamines such as, for example, triethylenediamine, N-methylmorpholine,N-ethylmorpholine, diethylethanolamine, N-cocomorpholine,1-methyl-4-dimethylaminoethylpiperazine, 3-methoxypropyldimethylamine,N,N,N'-trimethylisopropyl propylenediamine,3-diethylaminopropyldiethylamine, dimethylbenzylamine, and the like.Other suitable catalysts are, for example, stannous chloride, dibutyltindi-2-ethyl hexanoiate, stannous oxide, as well as other organometalliccompounds such as are disclosed in U.S. Pat. No. 2,846,408, incorporatedherein by reference.

A surface-active agent is generally necessary for production of highgrade polyurethane foam according to the present invention, since in theabsence of same, the foams collapse or contain very large uneven cells.Numerous surface-active agents have been found satisfactory. Non-ionicsurface active agents are preferred. Of these, the non-ionicsurface-active agents such as the well-known silicones have been foundparticularly desirable. Other surface-active agents which are operative,although not preferred, include polyethylene glycol ethers of long chainalcohols, tertiary amine or alkanolamine salts of long chain alkyl acidsulfate esters, alkyl sulfonic esters, and alkyl arylsulfonic acids.

If desired, flame retardants may be incorporated in the foams. Among theflame retardants which may be employed are: pentabromodiphenyl oxide,dibromopropanol, tris(b-chloropropyl)phosphate, 2,2-bis(-bromoethyl)1,3-propanediol, tetrakis(2-chloroethyl)ethyle diphosphate,bis-(2-chloroethyl) 2-chloroethylphosphonate, molybdenum trioxide,ammonium molybdate, ammonium phosphate, pentabromodiphenyl oxide,tricresylphosphate, hexabromocyclododecane and dibromoethyldibromocyclohexane. The concentrations of flame retardant compoundswhich may be employed range from 1 to 25 parts per 100 parts of polyolmixture.

Suitable methods of preparation include the prepolymer technique whereinan excess of organic polyisocyanate is reacted with a polyol to preparea prepolymer having free isocyanate reactive groups, which is thenreacted with a mixture of water, surfactant, and catalyst to obtain thefoam. Alternatively, one may employ the quasi-prepolymer techniquecommon in the preparation of rigid foams by reacting only a part of thepolyol with the organic polyisocyanate to obtain a quasi-prepolymer,which is then reacted with the remaining portion of polyol in thepresence of water, surfactant, and catalyst. Another option is toprepare a foam by reacting all the components in a single working stepknown as the "one-shot" method. In the one-shot method, the componentsmay be mixed in a mix head or by impingement mixing.

The polyurethane components combined by any one of the above-mentionedtechniques may be poured or sprayed into an open mold, which issubsequently closed and clamped, if necessary, to allow the componentsto fully react, after which the part is demolded and allowed to cure.Alternatively, the polyurethane components may be injected into an openor closed mold, which is subsequently closed if the components wereinitially injected into an open mold; and the components are allowed tofully react after which the part is demolded and set aside to cure.

Another advantage of the invention is that the open or closed mold maybe packed by pouring, injecting, or spraying the polyurethane componentsat a packing ratio of 1.7 or less to obtain a foam at the low givendensity; whereas, other water blown foams typically require packingratios of 2.0 to 8 to obtain foams with an open cell content at the samegiven density. The phrase "packing ratio" is defined herein as the ratioof the actual molded density to the free rise density. The low packingratio is made possible by incorporating a lithium salt into thepolyurethane foam formulation. The lower packing ratio decreases moldpressure, enhances safety, and reduces the amount of isocyanate consumedby the lowered quantity of water. Preferable packing ratios range from1.1 to 1.5, more preferably 1.1 to 1.3, to obtain foams having moldeddensities ranging from about 1.9 to 2.8, preferably about 1.9 to 2.4,more preferably about 1.9 to 2.3.

The mixed polyurethane components may also be poured, injected, orsprayed into open cavities or molds and allowed to free rise instead ofreacting in a closed mold, such as in the production of slab stock whichis cut into a desired shape, a pour-in-place method of applying rigidpolyurethane between panels used as the final part, or a pour-behindmethod of foaming.

When using the one-shot process, the lithium salts of the inventionshould be pre-dissolved in water, formic acid, or the polyol dependingon the solubility of the organic portion of the salt. Instead ofpre-dissolving the lithium salt prior to metering, the lithium salt maybe separately metered and added to the formulation as a solid. However,the salt must be milled to a fine dust as large granules fail to quicklydissolve in the formulation and fail to open up the cells of the foam.Regardless of which foaming method is employed, the prepolymer,one-shot, or quasi-prepolymer method, it is preferred to predissolve thelithium salt in either the polyol or water, most preferably dissolved inwater as a solution which is added to the resin side or dissolved informic acid as a solution which is added to the resin side.

The following examples illustrate various embodiments of the inventionand are not intended to limit the description of the invention above.The parts referred to in the examples are parts by weight. The followingabbreviations are employed:

Polyol A is an ethylene oxide-propylene oxide adduct of a mixture ofvicinal toluene diamine and dipropylene glycol containing apolyoxypropylene polyether cap and having an hydroxyl number of 450 andis commercially available from BASF Corporation as Pluracol® 1132polyol.

Polyol B is a vicinal toluene diamine initiated ethylene oxidepropyleneoxide adduct containing a 48 percent polyoxypropylene polyether caphaving a theoretical hydroxyl number of 390 and is commerciallyavailable from BASF Corporation as Pluracol® 824 polyol.

Polyol C is an all propylene oxide adduct of a mixture of sucrose andpropylene glycol having a theoretical hydroxyl number of 570 and iscommercially available from BASF Corporation as Pluracol® 240 polyol.

Polyol D is a sucrose-dipropylene glycol initiated all propylene oxideadduct having a theoretical hydroxyl number of 397 and is commerciallyavailable from BASF Corporation as Pluracol® 975 polyol.

Polyol E is a pentaerythritol-dipropylene glycol initiated all propyleneoxide adduct having a hydroxyl number of 555 and is commerciallyavailable from BASF Corporation as Pluracol® PEP 450 polyol.

Polyol F is a pentaerythritol-propylene glycol initiated all propyleneoxide adduct having a theoretical hydroxyl number of 450 and iscommercially available from BASF Corporation as Pluracol® PEP 550polyol.

Polyol G is a monoethanolamine ethylene oxide-propylene oxide adductcontaining a polyoxyethylene polyether cap and having a theoreticalhydroxyl number of 500 and is commercially available from BASFCorporation as Pluracol® 1016 polyol.

Polyol H is a glycerine initiated all propylene oxide adduct having atheoretical hydroxyl number of 398 and is commercially available fromBASF Corporation as Pluracol® GP 430 polyol.

Polyol I is a trimethylolpropane initiated propylene oxide adduct havinga theoretical hydroxyl number of 398 and is commercially available fromBASF Corporation as Pluracol® TP 440 polyol.

Polyol J is a propylene oxide adduct of ethylenediamine having atheoretical hydroxyl number of 767 and is commercially available fromBASF Corporation as Quadrol® polyol.

DEG is diethylene glycol having a theoretical hydroxyl number of 1016.

Polycat 8 is a dimethylcyclohexylamine (DMCHA) catalyst sold by AirProducts.

TMHDA is tetramethylhexanediamine, a urethane-promoting catalyst.

L-550 is a silicone surfactant commercially available from UnionCarbide.

DC-193 is a silicone surfactant sold by Dow Corning.

BiCat V is a bismuth based urethane promoting catalyst commerciallyavailable from Shepard Chemical employed to reduce tack free time.

ISO A is a solvent free polymethylene polyphenylisocyanate having afunctionality of about 2.7 and an NCO content of about 3I.8 weightpercent commercially available from BASF Corporation as LUPRANATE™ M205isocyanate.

Throughout the various examples and tables, those sample appearing withan asterisk (*) were made for comparison purposes. In Table I, samples1-4 compare the effect of lithium stearate on various rigid polyurethanefoams with identical formulations, each differing only in the amount oflithium stearate employed. Samples 5-11 examined the effect of 1.0 pbwlithium stearate salt at 1 pbw on rigid foam formulations employingdifferent polyols. The amount of water measured in parts by weightranged from about 6.6 to 8.4 to maintain a water concentration of 2weight percent based on the weight of the foam formulation.

Lithium stearate was dissolved in a mixture of polyols and DEG in theamounts shown in Table I. To this mixture was added the catalyst,surfactant, and water in the amounts shown and stirred for about 30seconds. The isocyanate was then added to the resin in the amount shownin Table I, the mixture stirred for seven seconds, and allowed to foamfreely. The free rise densities are recorded on Table I.

Portions of the batches from each of the hand-mixed samples were pouredinto open preheated 9"×9"×1" metal molds at the designated temperaturesand subsequently plugged. After demolding the rigid foams, their moldedpart densities were measured and recorded, along with the packing ratio,as shown in Table I below. The compressive strengths of the moldedsamples were subsequently tested.

                                      TABLE 1                                     __________________________________________________________________________                   SAMPLE                                                                        1*     2      3      4      5      6                           __________________________________________________________________________    Polyol A       60     60     60     60                                        Polyol B                                   60                                 Polyol J                                                                      Polyol C                                          40                          Polyol D                                                                      Polyol E                                                                      Polyol F                                                                      Polyol G                                                                      Polyol H       35     35     35     35     35     35                          DEG            5      5      5      5      5      5                           LI. STEARATE   0      0.5    1      2      1      1                           WATER ACTUAL WT.                                                                             6.79   6.85   6.87   6.90   6.58   7.17                        WATER per 100 pbw polyol                                                                     7.14   7.21   7.23   7.26   6.92   7.54                        TMHDA          1.5    1.5    1.5    1.5    1.5    1.5                         UC L550        1      1      1      1      1      1                           TOTAL          107.79 109.85 110.37 111.40 110.08 110.67                      INDEX          110    110    110    110    110    110                         ISO A          231.9  232.9  233.1  233.6  219.0  248.0                       DESIRED % H.sub.2 O                                                                          2      2      2      2      2      2                           BROOKFIELD VISCOSITY                                                                         1010   950    975    1000   865    2360                        CPS @ 76 F.                                                                   SPINDLE        3      3      3      3      3      3                           SPEED          20     20     20     20     20     20                          READING        20.2   19.0   19.5   20.0   17.3   47.2                        FACTOR         50     50     50     50     50     50                          APPEARANCE     CLOUDY CLOUDY CLOUDY CLOUDY CLOUDY CLOUDY                      1 QT. CUP                                                                     RESIN          19.0   19.2   19.3   19.4   20.1   18.5                        ISO            41.0   40.8   40.7   40.6   39.9   41.5                        MIX (SEC)      7      7      7      7      7      7                           GEL (SEC)      36     38     36     36     42     48                          TACK FREE (SEC)                                                                              60     58     58            75     66                          CUP DENSITY    1.74   1.75   1.79   1.83   1.74   2.32                        9 × 9 × 2 PACKED PANEL                                            RESIN          28.6   28.8   26.9   29.1   30.1   27.8                        ISO            61.4   61.2   61.1   60.9   59.9   62.2                        ACTUAL WT., GRS.                                                                             43.2   42.8   47.4   46.6   45.6   57.4                        MOLDED DENSITY/PCF                                                                           2.08   2.06   2.28   2.24   2.19   2.76                        CORE DENSITY   1.73   1.54   1.52   1.75   1.48   2.35                        MOLD TEMP., F. 142    145    141    140    146    142                         PACKING RATIO  1.2    1.18   1.27   1.22   1.26   1.19                        __________________________________________________________________________                         SAMPLE                                                                         7      8      9      10     11                          __________________________________________________________________________           Polyol A                                                                      Polyol B                                                                      Polyol J                                   60                                 Polyol C                                                                      Polyol D       60                                                             Polyol E              60                                                      Polyol F                     60                                               Polyol G                            60                                        Polyol H       35     35     35     35     35                                 DEG            5      5      5      5      5                                  LI. STEARATE   1      1      1      1      1                                  WATER ACTUAL WT.                                                                             6.63   7.35   6.87   7.11   8.39                               WATER per 100 pbw polyol                                                                     6.97   7.73   7.23   7.48   8.83                               TMHDA          1.5    1.5    1.5    1.5    1.5                                UC L550        1      1      1      1      1                                  TOTAL          110.13 110.85 110.37 110.61 111.89                             INDEX          110    110    110    110    110                                ISO A          221.3  256.6  233.1  244.9  307.7                              DESIRED % H.sub.2 O                                                                          2      2      2      2      2                                  BROOKFIELD VISCOSITY                                                                         780    534    430    272    1000                               CPS @ 76 F.                                                                   SPINDLE        3      3      3      3      3                                  SPEED          20     50     50     50     50                                 READING        15.6   26.7   21.5   13.6   50                                 FACTOR         50     20     20     20     20                                 APPEARANCE     CLOUDY CLOUDY CLOUDY CLOUDY CLOUDY                             1 QT. CUP                                                                     RESIN          19.9   18.1   19.3   18.7   16.0                               ISO            40.1   41.9   40.7   41.3   44.0                               MIX (SEC)      7      7      7      7      7                                  GEL (SEC)      59     61     63     27     28                                 TACK FREE (SEC)                                                                              115    86     120    38     35                                 CUP DENSITY    1.89   1.57   1.83   1.85   1.90                               9 × 9 × 2 PACKED PANEL                                            RESIN          29.9   27.1   28.9   28.0   24.0                               ISO            60.1   62.9   61.1   62.0   66.0                               ACTUAL WT., GRS.                                                                             48.2   38.6   48.2   50.4   48.3                               MOLDED DENSITY/PCF                                                                           2.32   1.86   2.32   2.42   2.32                               CORE DENSITY   1.79   1.6    1.66   1.65   1.71                               MOLD TEMP., F. 140    140    136    140    136                                PACKING RATIO  1.23   1.18   1.27   1.31   1.22                        __________________________________________________________________________

The molded foam samples were cut into squares measuring 2 inches wide, 1inch long, and 2 inches thick and tested for compressive strength at 10percent deflection intervals according to ASTM D-1621 at a crossheadspeed of 0.3 inches/minute, 50 percent humidity, and 73° F. The numberscorresponding to each sample represent an average value taken from threespecimens.

                                      CHART I                                     __________________________________________________________________________                  STRENGTH                                                                             STRENGTH                                                                             STRENGTH                                                                             STRENGTH                                          STRENGTH                                                                             AT 10% AT 20% AT 30% AT 40%                                     SAMPLE AT YIELD                                                                             CRUSH  CRUSH  CRUSH  CRUSH                                      NO.    (psi)  (psi)  (psi)  (psi)  (psi)                                      __________________________________________________________________________     1*    --     8.26   11.24  13.06  14.82                                      2      13.59  12.81  14.36  15.42  16.87                                      3      14.29  11.43  13.86  15.04  16.14                                      4      13.25  12.57  13.56  14.57  15.61                                      5      12.29  10.86  12.56  13.61  15.27                                      6      21.04  14.70  18.05  20.33  22.34                                      7      14.62  14.41  16.41  18.86  21.73                                      8      10.05  9.54   10.42  11.81  13.97                                      9      --     14.58  18.68  21.9   24.48                                      10     10.63  9.90   11.28  12.31  13.95                                      11     11.15  10.36  11.51  13.11  16.85                                      __________________________________________________________________________                  STRENGTH                                                                             STRENGTH                                                                             STRENGTH                                                                             STRENGTH                                                 AT 50% AT 60% AT 70% AT 80%                                             SAMPLE                                                                              CRUSH  CRUSH  CRUSH  CRUSH                                              NO.   (psi)  (psi)  (psi)  (psi)                                      __________________________________________________________________________             1*   18.73  27.18  41.03  77.22                                              2     19.05  23.14  31.54  55.42                                              3     18.95  23.52  31.67  56.43                                              4     17.36  21.89  32.71  60.48                                              5     18.07  22.08  31.71  58.45                                              6     27.20  37.28  51.01  96.65                                              7     25.24  29.83  37.78  64.27                                              8     17.01  20.6   26.58  42.84                                              9     27.69  31.29  39.05  68.33                                              10    17.21  21.7   30.68  55.73                                              11    22.13  29.51  37.97  69.02                                      __________________________________________________________________________

FIG. 1 graphically illustrates the data points for the values set forthfor Samples 1*-4 in Chart I and demonstrates that the constancy of thecompressive strengths at deflections ranging from 10 percent to 60percent for rigid foam Samples 2-4 employing lithium stearate isimproved a rigid foam Sample 1* without lithium stearate havingidentical types of polyols, isocyanate, catalyst, surfactant, and totalamounts of water, at molded densities less than 2.3 pcf, water contentsless than 7 pbw, and packing ratios ranging from 1.18 to 1.27.

Chart I and FIG. 1A also show that lithium stearate imparts energyabsorbing characteristics to water blown rigid foams made with a widerange of polyols as in Samples 5-11. The water content in parts byweight was varied to maintain a constant 2 weight percent water contentbased on the weight of the whole formulation.

EXAMPLE 2

In this Example, the effects of lithium acetate, commercially availablefrom FMC Corporation--Lithium Division in North Carolina, and a mixtureof lithium acetate and ammonium formate on the constancy of compressivestrength were examined. For comparison purposes, water blown Samples16-22 were prepared at various free rise densities and their compressivestrengths tested. The type and amount of ingredients as shown in TableII were hand mixed according to the procedure of Example 1. Lithiumacetate was dissolved in water prior to addition to the resin. Samples12, 13, and 16-22 were poured into quart cups and allowed to free rise,and samples 14, 15, and 23 were poured into a 4"×10"×10" cake box,plugged, and subsequently demolded upon completion of the reaction.

                                      TABLE II                                    __________________________________________________________________________                   SAMPLE NO.                                                                    12  13  14  15  16* 17* 18* 19* 20* 21* 22* 23                 __________________________________________________________________________    Polyol A       60  60  60  60  60  60  60  60  60  60  60  60                 Polyol H       40  40  40  40  40  40  40  40  40  40  40  40                 DC-193         1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5                Polycat 8      1.5 1.5 1.5 1.5 0.2 0.2 0.2 0.2 0.2 0.2 0.2 1.5                BiCat V        --  --  --  --  0.2 0.2 0.2 0.2 0.2 0.2 0.2 --                 Lithium Acetate.sup.(a) Sol.                                                                 10.04                                                                             7.27                                                                              7.27                                                                              8.05                                                                              --  --  --  --  --  --  --  5.22               LiOAC/100 pbw polyol                                                                         3.54                                                                              2.56                                                                              2.56                                                                              2.84                                                                              --  --  --  --  --  --  --  1.84               Ammonium Formate.sup.(b) Sol.                                                                --  --  --  --  --  --  --  --  --  --  --  3.19               Water          --  1.80                                                                              0.08                                                                              0.09                                                                              3.0 3.5 4.0 4.5 5.0 5.5 6.0 2.25               Water per 100 pbw polyol                                                                     6.50                                                                              6.50                                                                              4.78                                                                              4.78                                                                              3.0 3.5 4.0 4.5 5.0 5.5 6.0 7.0                ISO A          229.1                                                                             229.2                                                                             197.1                                                                             218.3                                                                             161 169 177 185 193 202 210 231.1              Index          115.7                                                                             115.7                                                                             114 114 110 110 110 110 110 110 110 105.6              Mix Time (s)   7   7   7   7   7   7   7   7   7   7   7   7                  Cream Time (s) 14  13  --  --  24.5                                                                              26.2                                                                              30.3                                                                              28.8                                                                              33.4                                                                              32.3                                                                              32.6                                                                              --                 Gel Time (s)   40  38  --  --  72  79  94  90  105 113 108 --                 Rise Time (s)  65  65  --  --  118 139 159 174 158 173 162 --                 Tack Free (s)  54  51  --  --  108 122 146 169 198 242 214 --                 Free Rise Cup Density (pcf)                                                                  1.54                                                                              1.48                                                                              --  --  3.37                                                                              3.12                                                                              2.76                                                                              2.52                                                                              2.29                                                                              2.18                                                                              2.12                                                                              --                 Free Rise Core Density (pcf)                                                                 1.32                                                                              1.30                                                                              --  --  3.06                                                                              2.32                                                                              2.21                                                                              2.09                                                                              1.90                                                                              1.59                                                                              1.56                                                                              --                 Molded Density (pcf)                                                                         --  --  2.47                                                                              2.80                                                                              --  --  --  --  --  --  --  1.74               Molded Core Density (pcf)                                                                    --  --  2.2 2.45                                                                              --  --  --  --  --  --  --  1.65               __________________________________________________________________________     .sup.(a) a solution of lithium acetate obtained by dissolving 120 g           LiOAc.2H.sub.2 O in 100 g water, yielding 35.29 percent LiOAc and 64.71       percent water including dihydrate.                                            .sup.(b) 150 g ammonium formate dissolved in 200 g H.sub.2 O (42.86%          H.sub.2 O).                                                              

Each foam sample was tested for compressive strength according to ASTMD-1621 using cut 3" wide, about 1" long, and 3" thick specimens at acrosshead speed of 0.3 in/min., 50 percent humidity, and 73° F.

The results obtained from the tests are reported on Chart II below andthe values for Samples 12, 13, and 16 represent an average of twospecimens; those for Samples 14 and 15 represent a test performed on onespecimen.

                                      CHART II                                    __________________________________________________________________________                  STRENGTH                                                                             STRENGTH                                                                             STRENGTH                                                                             STRENGTH                                          STRENGTH                                                                             AT 10% AT 20% AT 30% AT 40%                                     SAMPLE AT YIELD                                                                             CRUSH  CRUSH  CRUSH  CRUSH                                      NO.    (psi)  (psi)  (psi)  (psi)  (psi)                                      __________________________________________________________________________    12     18.71  19.48  19.56  19.67  19.85                                      13     17.55  18.70  19.38  19.27  19.56                                      14     42.4   43.25  43.71  44.58  45.19                                      15     49.54  50.27  51.00  50.65  50.29                                      16*    --     34.86  36.28  38.78  42.15                                      17*    --     26.47  28.65  31.17  34.56                                      18*    --     20.67  22.29  24.67  27.85                                      19*    --     16.63  18.18  20.45  23.37                                      20*    --     15.16  16.58  18.60  21.28                                      21*    --     12.95  14.58  16.67  19.52                                      22*    --     11.43  12.80  14.74  17.39                                      23     34.89  35.14  34.74  35.11  35.71                                      __________________________________________________________________________                  STRENGTH                                                                             STRENGTH                                                                             STRENGTH                                                                             STRENGTH                                                 AT 50% AT 60% AT 70% AT 80%                                             SAMPLE                                                                              CRUSH  CRUSH  CRUSH  CRUSH                                              NO.   (psi)  (psi)  (psi)  (psi)                                      __________________________________________________________________________            12    19.75  19.94  20.64  28.49                                              13    19.94  20.41  21.42  32.69                                              14    45.69  45.86  48.42  71.12                                              15    50.70  51.82  53.64  86.72                                              16*   47.54  58.24  79.41  135.5                                              17*   40.06  49.82  68.21  113.0                                              18*   32.58  41.41  57.58  95.33                                              19*   27.65  35.48  49.49  79.14                                              20*   25.16  32.17  45.24  73.5                                               21*   23.88  31.11  43.92  71.31                                              22*   21.02  27.37  39.20  63.13                                              23    36.65  37.84  40.21  49.56                                      __________________________________________________________________________

FIG. 2 graphically illustrates the flatness of curves from 10 percentdeflection to 60 percent deflection for lithium acetate containingSamples 11-15 and 23; and by comparison, FIG. 2A shows the much largerdeviations in compressive strengths for comparative Samples 16*-22*which were water blown without any lithium salts.

The results from Chart II and illustrated in FIG. 2 demonstrate aconstant compressive strength for water blown Samples 12-15 and 23containing lithium salts with deviations between 10 percent to 60percent deflections of less than 0.5 psi for Sample 12, less than 1.8psi for Sample 13, less than 2.7 psi for Sample 14 at a molded densityof 2.47 pcf and a water content of less than 5 pbw/100 pbw polyol, lessthan 1.6 psi for Sample 15 at a 2.8 pcf molded density and a watercontent of less than 5 pbw/100 pbw polyol, and a deviation of 2.7 psifor Sample 23 at a 1.74 pcf molded density and a water content of 7pbw/100 pbw polyol.

The advantage in constancy of compressive strength obtained by usinglithium salts is readily apparent upon comparison of Samples 16*-22*with Samples 12-15. The molded Samples 14 and 15 having molded densitiesof 2.47 pcf and 2.80 pcf exhibit much flatter curves than do Samples18*-22* having similar free rise densities from 2.12 pcf to 2.76 pcf.One would expect a molded part to have a greater closed cell content andthus an inferior compressive strength profile to a free rise sample atthe equivalent density. Nevertheless, by incorporating lithium saltsinto the formulation, the tests demonstrate a great improvement in theconstancy of compressive strengths of lithium salt containing foams,even molded foams, over non-lithium salt containing foams at the samedensity. Furthermore, a comparison between the free rise densities ofSamples 12 and 13 and Sample 22* shows that about the same amount ofwater content, systems containing lithium acetate produced foams havinglower densities and much flatter compressive strength curves.

A comparison of the curves from FIG. 1 and FIG. 2 shows that althoughlithium stearate improved the compressive strength characteristics ofthe molded foam as shown in Samples 2-4 over the same foam withoutlithium stearate as in Sample 1*, molded Samples 14 and 15 yielded agreater improved performance by using lithium acetate over lithiumstearate. A mixture of lithium acetate and ammonium formate also yieldedexcellent flat compressive strength curves.

EXAMPLE 3

In this example, the effect of lithium acetate on molded samplesmanufactured by a low pressure ADMIRAL machine using the one-shotprocess was examined. Molded samples having the same kinds and amountsof ingredients but at various densities were also compared to eachother. The parameters were as follows:

    ______________________________________                                        Machine              Low Pressure                                             Component Temperature                                                         Resin °C.      24                                                      Isocyanate °C.                                                                               22                                                      Mixing Pressure                                                               Resin (psi)           80                                                      Isocyanate (psi)     100                                                      Throughput lbs./min.  14.3                                                    Processing Mode      Open Mold Pour                                           ______________________________________                                    

The types and amounts of ingredients were shot according to theformulation below in Table III. Except for Sample 17 which was shot intoa five-gallon payliner, the formulations were shot into a 4"×10"×10"cake box, plugged, and allowed to react to completion.

                  TABLE III                                                       ______________________________________                                               SAMPLE NO.                                                                    24    25      26      27    28    29                                   ______________________________________                                        POLYOL A 60      60      60    60    60    60                                 POLYOL H 40      40      40    40    40    40                                 DC 193   1.5     1.5     1.5   1.5   1.5   1.5                                POLYCAT 8                                                                              2.0     2.0     2.0   2.0   2.0   2.0                                LITHIUM  2.94    2.94    2.94  2.94  2.94  2.94                               ACETATE                                                                       SOL. (a)                                                                      FORMIC   4.39    4.39    4.39  4.39  4.39  4.39                               ACID                                                                          SOL. (b)                                                                      TOTAL    4.47    4.47    4.47  4.47  4.47  4.47                               WATER/                                                                        100 pbw                                                                       polyol                                                                        ISO A    188.8   188.8   188.8 188.8 188.8 188.8                              INDEX    105     105     105   105   105   105                                SHOT WT. 649.2   216.4   233.7 246.7 268.3 283.5                              (g)                                                                           SHOT     6.0     2.00    2.16  2.28  2.48  2.62                               TIME (s)                                                                      MOLDED   n/a     1.56    1.71  1.82  1.98  2.22                               DENSITY                                                                       (pcf)                                                                         MOLDED   1.32    1.29    1.36  1.43  1.54  1.68                               CORE                                                                          DENSITY                                                                       (pcf)                                                                         ______________________________________                                         (a) Solution of 41.1 g lithium acetate dihydrate in 100 g of water.           (b) Solution of 88.4 g formic acid (96% acid) in 100 g of water.         

Three specimens of each sample measuring 3" wide, 3" thick, and about 1"long were tested according to the procedures of Examples 1 and 2 at 73°F. and are set forth in Chart III below. Each value represents anaverage of the three tested specimens.

                                      CHART III                                   __________________________________________________________________________                  STRENGTH                                                                             STRENGTH                                                                             STRENGTH                                                                             STRENGTH                                          STRENGTH                                                                             AT 10% AT 20% AT 30% AT 40%                                     SAMPLE AT YIELD                                                                             CRUSH  CRUSH  CRUSH  CRUSH                                      NO.    (psi)  (psi)  (psi)  (psi)  (psi)                                      __________________________________________________________________________    24     16.46  16.47  16.47  16.65  17.15                                      25     25.37  25.11  25.52  25.46  25.83                                      26     26.74  26.89  26.99  27.90  27.43                                      27     29.93  30.11  30.11  30.20  30.77                                      28     31.49  31.52  31.10  31.46  32.37                                      29     34.88  34.85  34.35  35.32  36.80                                      __________________________________________________________________________                  STRENGTH                                                                             STRENGTH                                                                             STRENGTH                                                                             STRENGTH                                                 AT 50% AT 60% AT 70% AT 80%                                             SAMPLE                                                                              CRUSH  CRUSH  CRUSH  CRUSH                                              NO.   (psi)  (psi)  (psi)  (psi)                                      __________________________________________________________________________            24    18.44  21.39  27.88  45.9                                               25    26.24  26.72  30.15  49.0                                               26    27.65  28.52  32.82  53.8                                               27    31.09  32.03  36.57  59.8                                               28    33.78  36.14  42.02  70.0                                               29    38.57  41.09  43.69  69.3                                       __________________________________________________________________________

FIG. 3 shows the compressive strength curves for each of the machineshot molded samples at various densities. As can be seen from thecurves, the compressive strength constancy for machine-run moldedsamples at all the molded densities is well within ±10 psi and is withinonly ±2 psi at molded densities from 1.56 to 1.82.

EXAMPLE 4

In this example, the effect of lithium acetate on other polyols isexamined along with the effect that lithium acetate dissolved water vs.formic acid has on the constancy of compressive strength.

The foams of Samples 30-35 were mixed in quart cups, poured intoone-gallon cups, and allowed to free rise while the foams of Samples36-41 were poured into 4"×10"×10" cake boxes, plugged, allowed to reactto completion, and demolded. All foams were handmixed by the proceduredescribed in Example 1 using the types and amounts of ingredients alongwith the mix times set forth in Table IV below.

                                      TABLE IV                                    __________________________________________________________________________                  SAMPLE NO.                                                                    30   31  32  33  34  35  36  37  38  39  40  41                 __________________________________________________________________________    POLYOL C      50   50  50  50  50  50  45.5                                                                              44.7                                                                              46.9                                                                              48.5                                                                              44.75                                                                             46.9               POLYOL H      50   50  50  --  --  --  45.4                                                                              44.7                                                                              46.9                                                                              --  --  --                 POLYOL I      --   --  --  50  50  50  --  --  --  48.5                                                                              44.75                                                                             46.9               DC-193        0.6  0.6 0.6 0.6 0.6 0.6 0.55                                                                              1.53                                                                              0.56                                                                              0.59                                                                              0.53                                                                              0.56               LITHIUM ACETATE IN                                                                          9.09 --  7.46                                                                              9.09                                                                              --  7.46                                                                              8.27                                                                              --  6.99                                                                              8.82                                                                              --  6.99               FORMIC ACID (a)                                                               LITHIUM ACETATE IN                                                                          --   5.5 0.99                                                                              --  5.5 0.99                                                                              --  4.92                                                                              0.93                                                                              --  4.92                                                                              0.93               WATER (b)                                                                     FORMIC ACID   3.91 --  --  3.91                                                                              --  --  3.56                                                                              --  --  3.79                                                                              --  --                 WATER         --   3.7 2.65                                                                              --  3.7 2.65                                                                              --  3.32                                                                              2.48                                                                              --  3.32                                                                              2.48               WATER/100 pbw polyol                                                                        1.47 7.26                                                                              4.37                                                                              1.47                                                                              7.26                                                                              4.37                                                                              1.25                                                                              6.50                                                                              4.02                                                                              1.25                                                                              6.50                                                                              4.02               POLYCAT 8     --   1.0 --  --  1.0 --  --  0.90                                                                              --  --  0.90                                                                              --                 BiCat V       0.3  0.3 0.3 0.3 0.3 0.3 0.27                                                                              0.27                                                                              0.28                                                                              0.29                                                                              0.27                                                                              0.28               ISO A         172.6                                                                              199.8                                                                             186.2                                                                             172.6                                                                             199.8                                                                             186.2                                                                             157.1                                                                             178.9                                                                             174.7                                                                             167.4                                                                             178.9                                                                             167.4              INDEX         90   90  90  90  90  90  90  90  90  90  90  90                 MIX TIME (s)  10   8   8   8   8   8   8   8   8   8   8   8                  CREAM (s)     <10  29.1                                                                              18.7                                                                              17.2                                                                              23.6                                                                              20.9                                                                              --  --  --  --  --  --                 GEL (s)       14.4 85.7                                                                              105 55.1                                                                              93.5                                                                              113 --  --  --  --  --  --                 RISE (s)      49.8 130 152 89.8                                                                              124 176 --  --  --  --  --  --                 WEIGHT IN BOX (g)                                                                           --   --  --  --  --  --  207.2                                                                             232.1                                                                             234.6                                                                             219.5                                                                             231.7                                                                             228.9              DENSITY CUP (pcf)                                                                           1.56 1.89                                                                              2.13                                                                              1.70                                                                              1.90                                                                              1.80                                                                              --  --  --  --  --  --                 MOLDED DENSITY (pcf)                                                                        --   --  --  --  --  --  1.97                                                                              2.21                                                                              2.23                                                                              2.09                                                                              2.20                                                                              2.18               DENSITY CORE (pcf)                                                                          1.28 1.63                                                                              2.02                                                                              1.56                                                                              1.53                                                                              1.72                                                                              1.33                                                                              1.55                                                                              2.03                                                                              1.61                                                                              1.91                                                                              1.89               __________________________________________________________________________     (a) 50 g LiOAc.2H.sub.2 O in 100 g Formic Acid 96% (13.43% H.sub.2 O)         (b) 120 g LiOAc.2H.sub.2 O in 100 g water (64.7% H.sub.2 O)              

The samples were cut into 2" wide, 2" thick, 1" long sections and testedby the procedures described in Example 1. The results are set forthbelow and represent an average of three specimens for each reportedvalve.

                                      CHART IV                                    __________________________________________________________________________           STRENGTH                                                                             STRENGTH                                                                             STRENGTH                                                                             STRENGTH                                                                             STRENGTH                                                                             STRENGTH                                                                             STRENGTH                                                                             STRENGTH                     AT 10% AT 20% AT 30% AT 40% AT 50% AT 60% AT 70% AT 80%                SAMPLE CRUSH  CRUSH  CRUSH  CRUSH  CRUSH  CRUSH  CRUSH  CRUSH                 NO.    (psi)  (psi)  (psi)  (psi)  (psi)  (psi)  (psi)  (psi)                 __________________________________________________________________________    30     9.16   9.18   9.24   9.41   9.63   10.46  14.23  26.15                 31     9.11   9.88   10.13  10.66  11.86  14.34  20.24  38.03                 32     15.41  16.04  16.51  17.39  19.12  23.48  33.23  59.29                 33     16.07  16.94  16.83  16.93  17.33  19.30  26.20  46.94                 34     8.38   8.89   9.17   9.38   9.87   12.29  17.69  32.83                 35     14.38  14.47  14.64  15.16  16.33  19.68  27.35  47.64                 36     13.66  14.01  14.22  14.31  14.46  15.03  19.84  38.40                 37     7.91   8.27   8.67   9.18   10.22  12.70  18.74  36.88                 38     13.15  14.42  15.49  16.51  18.38  22.82  32.92  10.45                 39     18.01  18.30  18.67  19.05  19.64  20.79  26.51  50.81                 40     11.61  11.49  11.62  11.84  11.95  14.30  20.22  37.52                 41     13.26  14.00  14.77  15.32  16.82  21.32  30.73  55.04                 __________________________________________________________________________

The results of Samples 30-35 are graphically illustrated in FIG. 4, andthe results from Samples 36-41 are depicted in FIG. 4A. As can be seenfrom the results in the Charts and Figures, rigid polyuethane foamSamples 30-31, 33-37, and 39-40 made with a variety of polyols andlithium acetate exhibit constant compressive strength within ±6 psi atfree rise densities from 1.56 to 1.8 and at molded densities from about1.9 to about 2.2. A comparison between the pitch of each curve alsosuggests that best results are generally obtained by dissolving lithiumacetate in formic acid without employing lithium acetate dissolved inwater as shown by Samples 30, 33, 36, and 39. As shown by Samples 31,34, 37, and 40, dissolving lithium acetate in water without employingformic acid also yielded a foam with constant compressive strengths butgenerally not quite as constant as foams having lithium acetatedissolved in formic acid. Sample foams 32, 38, and 41 exhibited nearlyconstant compressive strength, but the combination of a solution oflithium acetate dissolved in formic acid, a solution of lithium acetatedissolved in water, and additional water-produced foams with the poorestcompressive strength curves out of Samples 23-34. All foams weresuitable for energy absorbing applications.

EXAMPLE 5

The following example compares the effect of formic acid-blown rigidpolyurethane foam systems having no lithium salts, solid lithiumacetate, and lithium acetate dissolved in formic acid upon the constancyof compressive strengths. The samples were handmixed as in Example 1using the types and amounts of ingredients shown below in Table V. Thesamples were poured into quart cups and allowed to free rise.

                                      TABLE V                                     __________________________________________________________________________                 SAMPLE NO.                                                                    42* 43* 44* 45  46  47  48  49  50                               __________________________________________________________________________    POLYOL A     60  60  60  60  60  60  60  60  60                               POLYOL H     40  40  40  40  40  40  40  40  40                               DC-193       1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5                              POLYCAT 8    0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2                              LiOAc.2H.sub.2 O                                                                           --  --  1.53                                                                              --  --  --  --  --  --                               (solid).sup.(a)                                                               LiOAc IN FORMIC                                                                            --  --  --  4.63                                                                              4.63                                                                              9.26                                                                              9.26                                                                              4.63                                                                              4.63                             ACID.sup.(b)                                                                  FORMIC ACID  7.0 7.0 7.0 3.90                                                                              3.90                                                                              0.80                                                                              0.80                                                                              6.90                                                                              6.90                             (96%)                                                                         BiCat V      --  0.2 0.2 0.2 --  --  0.2 0.2 --                               WATER/100 pbw polyol                                                                       0.28                                                                              0.28                                                                              0.82                                                                              0.82                                                                              0.82                                                                              1.37                                                                              1.37                                                                              0.94                                                                              0.94                             m Moles LiOAc/                                                                             --  --  15  15  15  30  30  15  15                               100 pbw polyol                                                                ISO A        152 152 161 161 161 169 169 180 180                              INDEX        105 105 105 105 105 105 105 105 105                              MIX TIME (s) 7   5   5   5   5   5   5   5   5                                CREAM TIME (s)                                                                             <7  <7  <7  <6  <6  <6  <6  <5  <5                               GEL TIME (s) 99  47  40  36  52  51  46  27  41                               RISE TIME (s)                                                                              147 81  80  85  111 104 89  53  116                              CUP DENSITY (pcf)                                                                          2.20                                                                              2.21                                                                              2.16                                                                              1.92                                                                              1.80                                                                              1.73                                                                              1.80                                                                              1.54                                                                              1.46                             CORE DENSITY (pcf)                                                                         2.05                                                                              1.93                                                                              1.80                                                                              1.55                                                                              1.45                                                                              1.38                                                                              1.39                                                                              1.20                                                                              1.14                             __________________________________________________________________________     .sup.(a) ground fine with mortar and pestle                                   .sup.(b) 50 g LiOAc.2H.sub.2 O in 100 g formic acid (32.3% water includin     water of hydration)                                                      

The samples were cut into 2" wide, 2" thick, and I" long specimens andtested for their compressive strengths according to the procedure ofExample 2. The results reported below are an average of three specimenstested from each sample:

                                      CHART V                                     __________________________________________________________________________           STRENGTH                                                                             STRENGTH                                                                             STRENGTH                                                                             STRENGTH                                                                             STRENGTH                                                                             STRENGTH                                                                             STRENGTH                                                                             STRENGTH                     AT 10% AT 20% AT 30% AT 40% AT 50% AT 60% AT 70% AT 80%                SAMPLE CRUSH  CRUSH  CRUSH  CRUSH  CRUSH  CRUSH  CRUSH  CRUSH                 NO.    (psi)  (psi)  (psi)  (psi)  (psi)  (psi)  (psi)  (psi)                 __________________________________________________________________________     42*   18.69  19.50  21.26  23.86  27.18  32.75  44.01  71.87                  43*   13.78  18.13  17.32  20.28  24.34  31.48  46.00  80.54                  44*   13.48  14.91  17.05  20.02  24.03  31.12  44.91  78.26                 45     11.44  11.86  12.48  13.28  14.39  16.87  23.14  42.08                 46     11.93  11.73  12.24  12.81  13.83  16.09  21.56  38.28                 47     9.28   9.74   10.13  10.62  11.57  14.64  21.70  41.30                 48     8.77   8.88   9.14   9.53   10.46  12.97  18.48  35.18                 49     6.84   8.43   9.09   9.72   10.45  11.39  14.34  25.09                 50     6.61   7.61   8.29   8.73   9.32   10.29  12.95  22.26                 __________________________________________________________________________

The test results for comparative Samples 42*-44* are graphicallyillustrated in FIG. 5 while those of inventive Samples 45-50 are shownin FIG. 5A. As can be seen from the curves, it is the presence oflithium salts, not formic acid, that causes the compressive strength tobecome constant or nearly constant. Foam Samples 42* and 43* preparedwith formic acid and without lithium salts exhibited sharp increases incompressive strengths with increasing deflection for deviations greaterthan 14 p.s.i. The presence of BiCat V failed to have a positiveinfluence on the pitch of the curve. Adding hand-ground lithium acetatedihydrate to the resin and mixing for five seconds in Sample 44* failedto thoroughly dissolve the lithium acetate; furthermore, it performed aspoorly as foams made without lithium acetate having a deviation ofgreater than 17 p.s.i. at 10% to 60% deflection. However, dissolvinglithium acetate in formic acid prior to blending with the resin resultedin a rigid foam exhibiting constant compressive strength throughdeflections ranging from 10 percent to 60 percent as shown by the curvecorresponding to Samples 45 and 46. The remaining samples were preparedto test the effect that differing proportions of lithium acetate andformic acid had on the constancy of compressive strength. The testresults obtained from Samples 47 and 48 and Samples 49 and 50 indicatedthat the differing ratios between lithium acetate and formic acid in theproportions tested do not significantly impact the performances of thefoam. However, between these samples tested, higher proportions offormic acid yielded slightly flatter curves than the samples preparedwith higher proportions of lithium acetate.

Without being limited to a theory, one of the factors accounting forthis difference may be attributable not so much to the ratio betweenformic acid and lithium acetate as formulated but, perhaps, to thedensities of the foam samples. The number of broken struts and foamparticles below the crushing head or object increases as the headadvances through the foam resulting in an increase in resistance and agreater force necessary to further deflect the foam. Accordingly, therate of resistance against the head or object approaching 60 percentdeflection on a foam with low density will not be as great as the rateof resistance encountered by a head approaching 60 percent deflection ona higher density foam.

EXAMPLE VI

The foams in this Example were handmixed by the procedure set forth inExample 1 in the proportion and amounts set forth below in Table VI. Theratio of Polyol A to Polyol H remained constant at 1.5. Thesecompositions reported in the Table VI further set forth alternativeformulation to make rigid foams exhibiting compressive strengths varyingnot more than ±6 psi at deflections from 10 percent to 60 percent and atmolded densities less than 2.2 pcf. The handmixed batches were pouredinto 4"×10"×10" wooden cake boxes, plugged, and allowed to react. Thedensity of each sample is set forth in the table below:

                  TABLE VI                                                        ______________________________________                                                       SAMPLE NO.                                                                    51    52      53      54                                       ______________________________________                                        POLYOL A         61.2    73.8    60.6  66.6                                   POLYOL H         40.8    49.2    40.4  44.4                                   DC-193           1.53    1.85    1.51  1.66                                   POLYCAT 8        0.20    0.25    0.20  0.22                                   LiOAC.2H.sub.2 O IN FORMIC                                                                     4.72    5.69    4.68  3.14                                   ACID (96%).sup.(a)                                                            FORMIC ACID (96%)                                                                              3.98    4.80    0.70  7.66                                   BiCat V          0.20    0.25    0.20  0.22                                   WATER/100 pbw POLYOL                                                                           0.82    0.82    1.37  0.94                                   ISO A            164     170     180   198                                    INDEX            105     90      105   105                                    MOLDED DENSITY (pcf)                                                                           1.96    2.13    2.16  2.03                                   ______________________________________                                         .sup.(a) 50 g LiOAC.2H.sub.2 O in 100 g 96% Formic Acid (13.43% water)   

The same procedure used to test the samples of Example 2 were employedhere. The results are reported below in Chart VI as an average of threespecimens per sample.

                                      CHART VI                                    __________________________________________________________________________           STRENGTH                                                                             STRENGTH                                                                             STRENGTH                                                                             STRENGTH                                                                             STRENGTH                                                                             STRENGTH                                                                             STRENGTH                                                                             STRENGTH                     AT 10% AT 20% AT 30% AT 40% AT 50% AT 60% AT 70% AT 80%                SAMPLE CRUSH  CRUSH  CRUSH  CRUSH  CRUSH  CRUSH  CRUSH  CRUSH                 NO.    (psi)  (psi)  (psi)  (psi)  (psi)  (psi)  (psi)  (psi)                 __________________________________________________________________________    51     15.42  15.65  16.19  16.87  17.59  18.66  21.48  39.28                 52     14.92  15.62  16.12  17.20  18.85  21.23  26.79  45.40                 53     13.82  14.30  14.52  15.50  15.38  16.26  19.24  38.2                  54     18.94  20.14  21.06  21.97  23.02  24.77  27.25  44.8                  __________________________________________________________________________

As can be seen from FIG. 6, each of the sampled formulations (5I, 53,and 54) produced foams having constant compressive strengths anddeviations of less than ±6 psi with densities less than 2.2 at variouslevels of formic acid and isocyanate indices.

What is claimed is:
 1. A method of preparing an energy absorbing rigidpolyurethane open cell foamed article having a molded density of lessthan 2.8 pcf and a near constant compression strength of from about 10percent to about 60 percent deflection at loads of less than 60 psi,comprising;A) packing an open or closed mold with a formulation at apacking ratio less than 1.7; B) allowing the formulation to react in aclosed and optionally preheated mold, wherein the formulationingredients comprise:i) an organic polyisocyanate; ii) a compound havingat least two isocyanate reactive hydrogens; iii) a reactive blowingagent consisting essentially of water, formic acid, salts of formicacid, or mixtures thereof; iv) a urethane promoting catalyst; v) asurfactant; vi) a lithium salt of an organic material having 2 to 30carbon atoms and at least one carboxylic acid as a cell opening agent;and C) demolding and curing said article.
 2. The method of claim 1,wherein the ingredients are combined by the one shot method, prepolymermethod, or the quasiprepolymer method; mixed; and poured or injectedinto the mold.
 3. The method of claim 1, wherein the packing ratio isless than 1.3.
 4. The method of claim 1, wherein the mold is preheatedfrom about 120° F. to about 180° F.
 5. The method of claim 1, whereinthe lithium salt comprises lithium acetate and/or lithium stearate. 6.The method of claim 5, wherein the reactive blowing agent is water andthe lithium salt is premixed with all or a part of said water.
 7. Themethod of claim 1, wherein the amount of lithium salt is from 0 01 to3.0 parts by weight based on 100 parts by weight of the compound havingat least two isocyanate reactive hydrogens.
 8. The method of claim 1,wherein said reactive blowing agent consists essentially of water. 9.The method of claim 1, wherein the foam has a molded density less thanabout 2.3 pounds per cubic foot.
 10. The method of claim 1, wherein thearomatic organic isocyanate is selected from the group consisting ofcrude diphenyl methane diisocyanate, 4,4'-diphenylmethane diisocyanate,mixtures of 4,4'- and 2,4'-diphenylmethane diisocyanate, polymethylenepolyphenylene diisocyanate, modified diphenylmethane diisocyanates, andmixtures thereof.
 11. The method of claim 1, wherein the foam has aconstant compression strength from about 10 percent to about 60 percentdeflection at loads of less than 60 psi.
 12. The method of claim 11,wherein the foam has a molded density of less than 2.3 pounds per cubicfoot.
 13. The method of claim 12, wherein the foam has a molded densityfrom about 1.4 to about 2.2 pounds per cubic foot.
 14. A method ofpreparing a reactive blown polyurethane open cell foamed article havinga free rise density of 2.8 pcf or less obtained by mixing a formulationcomprising:i) an organic polyisocyanate, ii) a compound having at leasttwo isocyanate reactive hydrogens, iii) less than 8 parts by weightreactive blowing agent consisting essentially of water, formic acid,salts of formic acid, or mixtures thereof, based on 100 parts by weightof polyol, iv) a urethane promoting catalyst; v) a surfactant, and vi) alithium salt of an organic material having 2 to 20 carbon atoms and atleast one carboxylic acid as a cell opening agent; and allowing themixture to react and foam.
 15. The method of claim 14, wherein the mixedformulation is continuously or intermittently poured into an open moldand allowed to react and foam in an open mold.
 16. The method of claim15, wherein the mixed formulation is applied by a method selected fromthe group consisting of pouring, injecting, and spraying.
 17. The methodof claim 14, wherein the formulation is impingement mixed.
 18. Themethod of claim 14, wherein the free rise density of the foamed articleis less than 2.0 pounds per cubic foot.
 19. The method of claim 14,wherein the lithium salt is lithium acetate dissolved in said reactiveblowing agent, said foam having a nearly constant compressive strengthfrom 10 percent to about 60 percent deflection at loadings of less than60 psi.
 20. The method of claim 14, wherein the reactive blowing agentconsists essentially of water.